Although detection of arcs is desirable to reduce the possibility of a fire being ignited by an arc and to protect building wiring and consumer wiring, such as extension cords and appliance cords, as well as appliances themselves, known residential type circuit breakers typically do not include an arc detection unit. Arcs can generally be identified by the high frequency content of current in a branch circuit. High frequency current, i.e., current having a frequency exceeding the range of 1 KHz to 10 MHz, can be introduced into the branch circuit through benign apparatus such as universal motors in hair driers, drills, and vacuum cleaners. Such motors can produce significant high frequency energy due to arcing of the brush motor commutation. Silicon controlled rectifier lamp dimmers and advanced electronic devices can also generate high frequency energy. Discriminating between actual arcing faults and benign sources of high frequency energy is therefore more difficult than merely sensing a high frequency. A residential arc detection unit, however, must have a low nuisance trip rate, i.e., low false alarm rate. Known arc detection units having the necessary low false alarm rate are complex and therefore expensive.
To reduce the costs of arc detection units, some known circuit breakers include central processing units that execute algorithms to eliminate possible noise sources, such as electric household appliances and tools (e.g., motors, welders, switches). Such known algorithms include fourier analysis and other frequency domain based approaches. The noise sources are eliminated from the primary signal by classifying the noise resulting from such sources, and then using such classified signals to identify noise signals and sources in the primary signal. The noise signals are then subtracted from the primary signal so that the noise portion of the signal is eliminated.
The functional requirements for digital signal processing based on elimination of noise sources requires correct classification of noise signals followed by storage of data, i.e., storage of the primary signal portion associated with the noise signal. The processing power necessary to provide this function is high and increases linearly with the number of noise sources present as well as about with the square of the frequency range considered due to the Fourier Transform requirements.
It would be desirable to provide protection for a residence from arc type faults, including fault isolation and location. It would also be desirable to provide such protection at a low cost as compared to the costs associated with using sophisticated arc detection units.